The primary aim of this study is to utilise Messiah as a case study into Handel's creative process, attempting to examine details of its composition in chronological order, for the purposes of exposing and exploring Handel's creative decisions and methods. This means that the study is divided into chronological sections and, as the creation of the libretto of Messiah is inextricably linked to the creation of the musical work, the study begins with an investigation into the cultural precedents to the libretto of Messiah, the libretto's genesis and Charles Jennens's aim in (and method of) constructing it. Sketches and other 'pre-compositional' material form the next stage for discussion, raising the issue of Handel's well-known propensity to re-use his own and others' music. Handel's methods of creating the autograph score are then outlined in preparation for an analysis of the alterations that he made to the autograph during the work's initial composition. The focus then shifts towards the conducting score for an exploration of the various types of later alteration that some movements in particular were subjected to, examining Handel's reasons for selecting movements for alteration, the possible circumstances behind the changes and his methods of marking alterations in both the autograph and conducting scores, before assessing the role of these later alterations as part of the work's creation.